One way:
<b>Excel 2010</b><table cellpadding="2.5px" rules="all" style=";background-color: #FFFFFF;border: 1px solid;border-collapse: collapse; border-color: #BBB"><colgroup><col width="25px" style="background-color: #DAE7F5" /><col /><col /></colgroup><thead><tr style=" background-color: #DAE7F5;text-align: center;color: #161120"><th></th><th>A</th><th>B</th></tr></thead><tbody><tr ><td style="color: #161120;text-align: center;">1</td><td style="background-color: #BFBFBF;;">List</td><td style="background-color: #BFBFBF;;">Unique</td></tr><tr ><td style="color: #161120;text-align: center;">2</td><td style=";">a</td><td style=";">a</td></tr><tr ><td style="color: #161120;text-align: center;">3</td><td style=";">f</td><td style=";">f</td></tr><tr ><td style="color: #161120;text-align: center;">4</td><td style=";">g</td><td style=";">g</td></tr><tr ><td style="color: #161120;text-align: center;">5</td><td style=";">r</td><td style=";">r</td></tr><tr ><td style="color: #161120;text-align: center;">6</td><td style=";">f</td><td style="text-align: right;;">#N/A</td></tr><tr ><td style="color: #161120;text-align: center;">7</td><td style=";">g</td><td style="text-align: right;;">#N/A</td></tr><tr ><td style="color: #161120;text-align: center;">8</td><td style=";">a</td><td style="text-align: right;;">#N/A</td></tr></tbody></table><p style="width:3.6em;font-weight:bold;margin:0;padding:0.2em 0.6em 0.2em 0.5em;border: 1px solid #BBB;border-top:none;text-align: center;background-color: #DAE7F5;color: #161120">Sheet1</p><br /><br /><table width="85%" cellpadding="2.5px" rules="all" style=";border: 2px solid black;border-collapse:collapse;padding: 0.4em;background-color: #FFFFFF" ><tr><td style="padding:6px" ><b>Array Formulas</b><table cellpadding="2.5px" width="100%" rules="all" style="border: 1px solid;text-align:center;background-color: #FFFFFF;border-collapse: collapse; border-color: #BBB"><thead><tr style=" background-color: #DAE7F5;color: #161120"><th width="10px">Cell</th><th style="text-align:left;padding-left:5px;">Formula</th></tr></thead><tbody><tr><th width="10px" style=" background-color: #DAE7F5;color: #161120">B2</th><td style="text-align:left">{=INDEX(<font color="Blue">$A$2:$A$8,MATCH(<font color="Red">0,COUNTIF(<font color="Green">$B$1:B1,$A$2:$A$8</font>),0</font>)</font>)}</td></tr></tbody></table><b>Entered with Ctrl+Shift+Enter.</b> If entered correctly, Excel will surround with curly braces {}.
<b>Note: Do not try and enter the {} manually yourself</b></td></tr></table><br />